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DynamoDB Capacity Units Calculator

Work out dynamodb capacity units instantly with clear inputs, formula shown and shareable results.

About DynamoDB Capacity Units Calculator

A read capacity unit covers one strongly consistent read of up to 4 KB, halved for eventually consistent reads and doubled for transactional ones. A write capacity unit covers one write of up to 1 KB, so writes are far more expensive per byte — a 6 KB item costs 6 WCU to write but only 1.5 RCU to read eventually consistently.

Formula

Capacity units

RCU = reads x ceil(item KB / 4) x consistency multiplier (0.5 eventual, 1 strong, 2 transactional); WCU = writes x ceil(item KB) x (2 if transactional)

Worked example

With the default values below, DynamoDB Capacity Units Calculator returns Read capacity units required of 800. Change any input above and every figure here is recalculated in your browser.

Inputs used

Reads per secondminimum 0
800
Writes per secondminimum 0
250
Average item sizeaccepts 0.1–400 KB
6 KB
Read consistencyone of Eventually consistent, Strongly consistent, Transactional
Eventually consistent

Results

Read capacity units required
800 RCU
Write capacity units required
1,500 WCU
Monthly provisioned capacity cost
$787.67
Read units consumed per item
2

Step by step

  1. 1Values used
  2. 2Capacity units
  3. 3Read capacity units required= 800 RCU
  4. 4Write capacity units required= 1,500 WCU
  5. 5Monthly provisioned capacity cost= 787.67
  6. 6Read units consumed per item= 2

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why are writes so much more expensive?

The write unit granularity is 1 KB against 4 KB for reads, and writes must be replicated durably across three availability zones before acknowledgement.

Should items be kept small?

Yes. Capacity consumption is proportional to item size, so splitting rarely accessed attributes into a separate item or into object storage reduces cost substantially.

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